Sensorless brushless polyphase motors (SBPM's), particularly applicable to DC motors, are increasingly popular in consumer and industrial electronics because of their compact size, controllability, and high efficiency. For example, this type of motor including sensorless commutation eliminates costly position sensors, reducing complexity and improving reliability. In addition, sensorless brushless polyphase motors (SBPM's) have a longer life compared to conventional brush motors and achieve operation with reduced contamination of the motor and associated structures.
One shortcoming of SBPM's is that upon starting the motor, the position of the rotor with respect to a coil (stator) including two or more coils is unknown, requiring complex and time consuming starting algorithms to determine the position of the rotor so that proper synchronization of current or voltage to the coil may take place to reach operating speed. As a result, SBPM's may take longer than conventional motors to reach a rated operating speed than is desirable.
For example, in Sakurai et al. (U.S. Pat. No. 5,206,567), a sensorless brushless DC motor (e.g., spindle motor for rotating a magnetic recording medium) is started by positioning the rotor during a start up sequence of the motor where three coils are alternately excited and a rotor detection circuit is employed to sense rotor vibration and determine the rotor position prior to accelerating the motor to operating speed.
Carobolante et al. (U.S. Pat. No. 5,350,984) provide a method for start-up of a sensorless brushless DC motor where a threshold rotary speed of a rotor is first determined to determine an alignment of the rotor with respect to the coils prior to accelerating the motor to operating speed.
Cameron et al. (U.S. Pat. No. 5,572,097) provide a method and apparatus for starting a polyphase DC motor where a rotor is aligned in the motor in preparation for starting the motor where a first energization signal is applied to field coils of the motor in a first predetermined phase for a first predetermined time and then a second energization signal having a second predetermined phase displaced from the first phase by a predetermined amount is applied to the field coils for a second predetermined time period.
Nishimura et al. (U.S. Pat. No. 5,623,379) provide a method of controlling a start-up of a motor used for a disk apparatus where an aligning operation is performed immediately after the motor is stopped where the aligning operation rotates the rotor to a predetermined angular position relative to the stator. The alignment is performed after stopping the motor and then sending acceleration signals followed by a deceleration signal after a predetermined time period.
The prior art does not provide a method for aligning a sensorless brushless polyphase motor during a stopping operation to enable efficient alignment of the motor and to enable an efficient and pre-aligned subsequent start-up of the motor without alignment at the next instance of operation of the motor.
Thus, there is a need for an improved method for aligning a sensorless brushless polyphase motor during a stopping operation to enable efficient alignment of the motor and to enable an efficient and pre-aligned subsequent start-up of the motor without alignment at the next instance of operation of the motor, including with respect to motors where fast startup is critical, such as in motor vehicle fuel pumps.
Therefore it is an object of the invention to provide an improved method for aligning a sensorless brushless polyphase motor during a stopping operation to enable efficient alignment of the motor and to enable an efficient and pre-aligned subsequent start-up of the motor without alignment at the next instance of operation of the motor, including with respect to motors where fast startup is critical, such as in motor vehicle fuel pumps.